Slepian was born in Cambridge, Massachusetts, and raised in Rochester, New York; his grandfather was a Jewish immigrant from Russia. Slepian graduated from the University of Denver with a zoology degree but failed to be accepted to any American medical school. He graduated from Universidad Autónoma de Guadalajara medical school in 1978.

Dr. Slepian worked at Buffalo GYN Womenservices, Inc. in Buffalo, New York, providing abortion for members of the local and surrounding communities.[3] He also ran his own private OB/GYN practice in Amherst, New York, where he also resided. Slepian was quoted as saying, "Abortion is undeniably the taking of a human life. It is not pretty. It is not easy. And in a perfect world, it would not be necessary."

On October 23, 1998, Dr. Slepian had returned from synagogue, where he was attending a memorial service for his father, and was preparing soup in his kitchen when he was struck by a bullet fired through his window. The bullet shattered his spine and tore his aorta, barely missing his son's head as it exited. He died two hours later. Earlier that afternoon, Slepian's wife Lynne had forwarded a warning of potential attacks on her husband to a local police inspector.

Within days of Dr. Slepian's murder, pro-life groups rallied and staged clinic protests in Buffalo and Rochester, New York. While local leaders from both sides of the abortion debate decried these rallies as potential incitements to further violence, more extreme members of the pro-life community, such as Flip Benham of Operation Rescue, labeled calls for nonviolence "pitiful" and suggested that unless abortion was outlawed, "we are in store for more bloodshed in the streets—the likes of which will sicken even the sturdiest among us."

This murder was the climax of a series of five sniper attacks in four years in northern New York and Canada. Dr. Slepian was the fourth doctor and up to that time the seventh person in the USA to be murdered for performing abortions.

Following Dr. Slepian's murder, Kopp fled the U.S., but was arrested in France and extradited. He was tried and convicted of second-degree murder in Buffalo and is currently serving a 25 years to life term of imprisonment.